Wheel loader machines are used for moving material from one place to another at a worksite. These machines typically include an engine frame structure for housing the engine and having rear wheels driven by the engine, as well as for supporting an operator station for the operator. A non-engine frame structure with front wheels is attached to the engine frame structure by an articulated connection. A pair of lift arms coupled to the non-engine frame structure are raised and lowered by corresponding lift cylinders to adjust the elevation of an implement above the ground. The wheel loader machines may be able to move many different types of materials depending on the requirements of the job site. Consequently, the wheel loader machines may be designed to manipulate different types of implements.
Conventional wheel loaders are fitted with a geared transmission. However, wheel loaders with a hydrostatic continuous variable transmission have been steadily gaining popularity. One of the reasons for switching from a conventional powershift or geared transmission to a hydrostatic transmission is the fuel economy and high mileage achieved with a hydrostatic transmission. Generally speaking, a hydrostatic transmission includes a variable displacement pump that converts rotational power from a power source into fluid flow and a motor that converts the fluid flow back into rotational motion for driving a traction device of the work machine.
Notwithstanding the advantages of a hydrostatic transmission over conventional geared transmissions, a problem with the hydrostatic transmission arises when the wheel loader machine (having a hydrostatic transmission) stalls against an inanimate object, such as, a pile of rock, clay wall, and the like. When a geared transmission is stalled (e.g., exerting substantial force into the hit object without increasing transmission output speed, which is substantially zero), the geared transmission substantially lugs the engine of the wheel loader machine, where as a hydrostatic transmission does not lug the engine at all. This engine lug provides an audible feedback to the operator that the wheel loader machine is working and/or performing to its capacity, and is pushing or pulling as much as it possibly can. Since a hydrostatic transmission does not provide this feedback, the operator may get a sense that the work machine is not doing the same amount or quality of work.
It would accordingly be beneficial if a system for a hydrostatic transmission were developed that could emulate the engine lug of the geared transmission and provide feedback indicative of same to the operator of the work machine during stall conditions.